The invention relates generally to noise suppression techniques, and more particularly to systems and methods that provide improved sound attenuation properties.
The environmental noise caused by airplanes, automobiles, and other modern machinery can often be an annoyance. To maintain noise below acceptable levels, noise suppression techniques are often employed. Noise suppression has, therefore, become an important technology with a wide variety of industrial and residential applications. Noise suppression devices are often applied in heating ventilation and air conditioning (HVAC) systems, industrial machinery and complexes, transportation vehicles, and any machinery that may tend to produce unacceptably high levels of noise.
Accordingly, various devices and techniques exist for the suppression of noise. For example, to reduce the noise produced by heating and air conditioning systems, noise suppression devices are often fitted within ventilation ducts, ventilation intakes and exhausts, air extracts, etc. In the industrial setting, noise suppression technology is often applied to exhaust ducts, exhaust stacks, and air intake ducts to machinery such as compressors. To further reduce environmental noise, loud machinery is often contained within acoustic enclosures fitted with sound dampening barrier walls. To provide air circulation for acoustic enclosures while still reducing noise, vents are often equipped with acoustic hoods, louvers, silencers or some combination thereof.
The level of sound reduction, or attenuation, provided by such devices is often described in terms of the device's insertion loss. Insertion loss is the reduction in sound amplitude which results from inserting a sound-attenuating device in a sound conducting channel, and is often measured in decibels. In a test configuration wherein the sound amplitude is measured at the output of a sound conducting channel, insertion loss may be defined as a ratio of the sound amplitude without the sound-attenuating device inserted (A1) to the sound amplitude with the sound-attenuating device inserted (A2). This ratio may then be represented according to the following equation:Insertion loss (db)=20 log(A1/A2)
Typically, the insertion loss of such devices increases as the length of the device increases. Furthermore, to maintain acceptable air flow, the overall cross-sectional area of the device may be enlarged to compensate for the air flow resistance caused by the sound attenuation elements. Therefore, noise suppression equipment may tend to be bulky and expensive. As a result, it may be beneficial to provide a device with improved sound attenuation.